Method and machine for changing the curvature of elongated workpieces



Jan. 21, 1969 Filed July 21. 1966 H. LORENZ METHOD AND MACHINE FORCHANGING THE CURVATURE OF ELONGATED WORKPIECES Sheet of 6 D m aMIME/V701? Jan. 21, 1969 H. LORENZ 3,422,552

METHOD AND MACHINE FOR CHANGING THE. CURVATURE OF ELONGATED WORKPIECESFiled .July 21, 1966 Sheet N OI INVENTOP Hdkfil' ween z Jan. 21, 1969 H.LORENZ I METHOD AND MACHINE FOR CHANGING THE CURVATURE OF ELONGATEDWORKPIECES Filed July 21, 1966 7 Sheet 3 INVENTOR H0257 Law-W2 Jan. 21,1969 'H. LORENZ 3,422,652

METHOD AND MA NE FOR CHANG THE CURVATURE OF ONGATED WORK CES Filed July21, 1966 Sheet 5 of 6 W 15 /r/ \1 k j/A A J m \d I- 7W K it A J 1mJNVEIVTOR H0165; tail-NZ Jan. 21, 1969 H. LORENZ 3,422,552

1 METHOD AND M INE FOR CHANG THE CURVATURE ATED CES 0 LONG WORK FiledJuly 21, 1966 Sheet 6 of 6 L) Q k I g ID 0 @IO D A I l LT"? Q D Mlrewrokar zaeavz M424 a [JI f/hlm, A4? 4770!?5) United States Patent 3,422,652METHOD AND MACHINE FOR CHANGING THE CURVATURE 0F ELONGATED WORKPIECESHorst Lorenz, Solingen, Germany, assignor to Th. Kieserling & Albrecht,Solingeu, Germany Filed .luly 21, 1966, Ser. No. 567,010 Claimspriority, appliclzitiog Germany, Sept. 17, 1965,

1.7.5. or. 72164 24 Claims 1m. c1. BZld 1/02; B2111 13/08; B21d 21/00ABSTRACT OF THE DISCLOSURE The present invention relates to a method andmachine for changing the curvature of elongated workpieces. Moreparticularly, the invention relates to a method and machine forstraightening or bending of elongated metallic workpieces having arectangular, square or other noncircular cross-sectional outline. Stillmore particularly, the invention relates to a method and machine whichmay be applied to change the curvature of solid or tubular metallicworkpieces, especially of heavy-duty tubular workpieces havingcross-sectional dimensions, for example, in excess of two inches.

In accordance with presently known straightening methods, an elongatedmetallic workpiece is treated while advancing along a path defined byseveral sets of driven guide rolls. The application of straighteningforces takes place in accordance with the so-called triangle principlewhich means that two longitudinally spaced portions of a workpiece arekept in abutment with rigid supports and an intermediate portion of theworkpiece is subjected to stresses exceeding the elastic limit oftreated material so that the workpiece cannot recoil because itsmaterial undergoes permanent deformation. It was found that suchconventional methods are satisfactory only when the workpieces are nottoo heavy, i.e., if their cross-sectional area does not exceed a certainmaximum value. Also, the wall thickness of tubular workpieces plays animportant role in a bending or straightening operation because athin-walled workpiece is very likely to develop dents, depressions andsimilar undesirable flaws which appear at the point or points where thebending forces are applied thereagainst. Therefore, heavy-duty tubularworkpieces of other than circular outline are presently straightened byhand whereby the distance between such longitudinally spaced portionswhich are held against flexing while an intermediate portion undergoesdeformation must be very large so that the machines used for carryingout such conventional methods occupy too much room, especially in viewof the fact that their output is extremely low.

Accordingly, it is an important object of the present invention toprovide a novel and improved method of changing the curvature ofelongated metallic workpieces,

Patented Jan. 21, 1969 especially of tubular workpieces of rectangularor square cross-sectional outline, according to which such workpiecesmay be deformed to a desired extent, in a very simple and time savingmanner, and without any danger of denting or other undesirabledeformation of their walls or surfaces.

Another object of the invention is to provide a method of the justoutlined characteristics according to which the extent to which theworkpieces are being deformed (for example, straightened) may bedetermined and altered in the course of the actual bending orstraightening operation.

A further object of the invention is to provide a method of changing thecurvature of tubular metallic workpieces according to which the bendingor straightening operation can be carried out in a small area, byresorting to a very compact and relatively simple machine, and in such away that a series of workpieces may be treated in rapid succession andin a fully automatic way.

A concomitant object of the invention is to provide a machine which maybe utilized for carrying out the above outlined method and to constructand assemble the machine in such a way that its dimensions need notexceed the dimensions of conventional machines despite the fact that theimproved machine may be used for changing the curvature of exceptionallylong, heavy and thick-walled solid or tubular workpieces.

Still another object of the instant invention is to provide the improvedmachine with novel means for regulating the extent of deformation in thecourse of the actual bending or straightening operation.

A further object of my invention is to provide a machine of the aboveoutlined characteristics which can be readily and rapidly converted forbending or straightening of different types of workpieces.

Briefly stated, one feature of my present invention resides in theprovision of a method of changing the curvature of elongated workpieces,particularly to a method of straightening tubular workpieces having arectangular, square or other non-circular cross-sectional outline.Basically, the improved method comprises the steps of advancing theworkpieces seriatim and lengthwise along a predetermined path in whichthe workpieces are guided and moved by sets of cooperating advancing andwithdrawing rolls, subjecting successive portions of advancingworkpieces first to the action of initial bending forces to stress suchportions to slightly below the elastic limit of their material, andthereupon subjecting the initially stressed portions of successiveworkpieces to the action of additional or final bending forces to stresssuch portions beyond the elastic limit of their material and to thuseffect permanent deformation of the respective workpieces. It was foundthat such stepwise application of bending forces prevents denting oftubular workpieces at the points where the initial and/or additionalbending forces are applied thereto. The aforementioned sets of rollsalso serve to hold the workpieces against turning during travel alongthe predetermined path. The magnitude of additional or final bendingforces may be a small fraction of the magnitude of initial bendingforces and such initial bending forces may be applied in a plurality ofstages so that each successive portion of a workpiece advancing alongthe aforementioned path is subjected to stresses generated by more thantwo different bending forces. The initial and additional bending forcesmay be applied to successive portions of advancing workpieces in severaldirections so that the workpieces may be deformed in a plurality ofplanes whereby the deformation in one plane may but need not be the sameas in the other plane or planes. For example, the bending forces may beapplied in a horizontal and in a vertical plane, i.e., in two planeswhich make right angles with each other.

As a rule, the application of additional bending forces will take placeupon a portion of a traveling workpiece which is disposed between twoportions subjected to the action of initial bending forces. Themagnitude of initial and/or additional or final bending forces may bevaried while the workpieces travel along the aforementioned path.

The improved method is especially suited for bending or straightening ofnon-circular tubular workpieces; however, such method is equally usefulin connection with treatment of solid non-circular workpieces as well asin connection with the treatment of solid and/or tubular workpieces ofcircular cross-sectional outline.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved bending or straightening machine itself, however, both as toits construction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevational view of a straighteningmachine which embodies one form of my invention;

FIG. 2 is a top plan view of the straightening machine;

FIG. 3 is an end elevational view as seen from the left-hand side ofFIG. 1 or 2;

FIG. 4 is a transverse vertical section as seen in the direction ofarrows from the line AB of FIG. 1;

FIG. 5 is a transverse vertical section as seen in the direction ofarrows from the line C-D of FIG. 1;

FIG. 6 is an enlarged fragmentary section as seen in the direction ofarrows from the line E-F of FIG. 4;

FIG. 7 is a section as seen in the direction of arrows from the line G-Hof FIG. 6;

FIG. 8 is a fragmentary section as seen in the direction of arrows fromthe line I] of FIG. 6;

FIG. 9 is a diagram showing the mode of operation of the straighteningmachine which is illustrated in FIGS. 1 to 8; and

FIG. 10 is a similar diagram but showing the operation of a slightlymodified machine wherein the initial bending forces are applied in aplurality of stages.

Referring first to FIGS. 1 to 3, there is shown a straightening machinewhich comprises a base or bed In provided with two spaced supports orblocks 1 and 2. The block 1 supports three sets of driven feed rolls 3a,3b, 3c and the block 2 supports three sets of withdrawing rolls 3d, 32,3 These rolls together define an elongated horizontal path forworkpieces 37 (see FIG. 9) of rectangular or square cross-sectionaloutline. The rolls 3a-3f also serve as a means for advancing successiveworkpieces along the horizontal path.

The drive for the rolls 3a-3f comprises an electric motor 4 and aninfinitely variable-speed transmission 5 whose output shaft drives onepulley of a belt transmission 5a. A clutch 4a is interposed between themotor 4 and the input shaft of the transmission 5. The drive furthercomprises a gear box 7 which accommodates intermeshing gears (not shown)serving to drive three pairs of cardanic shafts 6 for the rolls 3a, 3b,3c. A motion transmitting spindle 10 connects the gear box 7 with asecond gear box 9 whose gears drive cardanic shafts 8 for the rolls 30.,3e, 3 All of the rolls 3a-3f are adjustable in directions toward andaway from each other so that the machine may treat workpieces ofdifferent rosssectional dimensions. The means for adjusting the rolls3a-3f with reference to the supports 1 and 2 is not shown in thedrawings. For example, all the upper rolls 3a-3c and 3d-3f can be movedsimultaneously nearer to or further away from the corresponding lowerrolls, or vice versa.

The machine further comprises a group of centrally located straighteningor bending rolls which form part of two stressing means for theworkpieces 37 and two groups of holding rolls 12. The group of rolls 12ais disposed between the two groups of rolls 12 and its purpose is tosubject the workpieces to the action of initial and additional or finalbending forces in a manner to be described in connection with FIG. 9.

As best shown in FIGS. 2 and 4, the group of rolls 12a comprises threesets of four rolls each and each such set of four rolls is mounted in acarrier 11a which is secured to a two-armed lever 13 by bolts 11a oranalogous removable fasteners. This enables the persons in charge torapidly convert the machine for treatment of different types ofworkpieces. The machine is furnished with several sets of carriers 11aeach provided with differently positioned and/ or dimensioned rolls 12a.

The arm 13a of each lever 13 has an opening (see FIGS. 6 and 7) whichaccommodates an annular adjusting member 14 surrounding a portion of asplined drive shaft 15. The adjusting member 14- accommodates a sleeve15a which is internally splined to rotate with the drive shaft 15, seeparticularly FIG. 7. The sleeve 15a has a slotted flange 15b, best shownin FIG. 8, which is rotatable in an antifriction bearing 15c provided ina hearing block 15d. The end portions of the drive shaft 15 are mountedin fixed bearing blocks 15a, 15] shown in FIG. 2. This shaft 15 isdriven by an electric motor 18 through an infinitely variable-speedtransmission 17 and a cardanic shaft 16 shown in the upper right-handportion of FIG. 2.

Each adjusting member 14 is shiftable in the axial direction of thedrive shaft 15 and is formed with two parallel external faces 14a, 1411Which are inclined with reference to the axis of the drive shaft andabut against two similarly inclined complementary internal faces of therespective eccentric ring 19. As shown in FIG. 6, each adjusting member14 is surrounded by one such eccentric ring 19 which is received in anantifriction hearing 20 fitted into the opening of the respective arm13a.

A round portion of each adjusting member 14 is received in antifrictionbearings 21 (see FIG. 6) for a rack 22 which meshes with a gear 24rotatable in a fixed 'frame 23 for the drive shaft 15. The gears 24 arerotatable by 'cardanic shafts 24a (see FIG. 2) Which receive motion fromreversible electric motors 24b. Rotation of gears 24 results in movementof respective adjusting members 14- in the axial direction of the driveshaft 15 with resultant change in the throw of the associated eccentricrings 19.

Each lever 13 is fulcrumed on a pivot 25 (see FIG. 4) which is mountedin a slide 26. The slides 26 are reciprocable in horizontal slots 27provided in the respective levers 13. Each pivot is further mounted in aforked bracket 2511 which is reciproca'ble in a dovetailed groovemachined into ways 28 provided on the base 1a. Each such bracket 25a isformed with a spindle nut 25b which meshes with a horizontal spindle 29rotatably mounted in the respective ways 28. The effective length ofeach arm of each lever 13 may be changed by rotating the associatedspindle 29 to thereby move the respective pivot 25 nearer to or furtheraway from the drive shaft 15. Depending on the direction in which aspindle 29 is rotated, the operator can change the path of movement ofrolls 12a during a revolution of the drive shaft 15. Such adjustment canbe carried out while the machine is in actual use.

Each group of holding rolls 12 also comprises two sets of four rollseach and each such set is mounted in a carrier 11 in a manner best shownin FIG 5. The carriers 11 are detachably secured to two-armed levers 30by means bolts 11. The levers 30 are fulcumed on horizontal pivots 31which are parallel to the pivots 25 and are mounted in brackets 32provided with spindle nuts 32a. The lower portion of each bracket 32 isslidable in a dovetailed groove provided in ways 33 carried by the base1a, and each of these ways 33 is provided with a horizontal spindle 34which meshes with the respective spindle nut 32a so that it can shiftthe associated bracket 32 toward and away from the spindle 10. Thelonger arms 30a of the levers 30 are formed with vertical bores forelongated adjusting bolts 35 which are turnable on pins 36 carried bythe base 1a and are provided with lock nuts 35a, 35b to hold the levers30 in selected positions of inclination. In this way, the operator canselect the exact level of the carriers 11, i.e., the distance betweenthe respective set of holding rolls 12 and the ground.

The operation of the machine shown in FIGS. 1 to 8 is as follows:

Prior to introducing the first workpiece 37 between the pairs of feedrolls 3a, 3b, 3c, the operators select the exact position of the holdingrolls 12 by manipulating the bolts 35 and nuts 35a, 35b (see FIG. 5) inorder to move the corresponding carriers 11 to a desired level above thefloor. As shown in FIG. 9, the holding rolls b (corresponding to therolls 12 of FIGS. 1, 2 and 5) may be located at the same level. Theoperators then adjust the position of the brackets 25a and 32 bymanipulating the corresponding spindles 29, 34 to thus select the exactposition of axes for the levers 13' and 30. The levers 13 will be rockedin response to rotation of the drive shaft 15. If necessary, theoperators also adjust the position of the adjusting members 14 bystarting the corresponding motors 24b. Once the levers 13 and 30 areproperly adjusted, the first workpiece 37 is introduced between the feedrolls a of FIG. 9 (corresponding to the feed rolls 3a, 3b, 3c of FIGS. 1to 3) so that the leading end of the workpiece is advanced between thetwo left-hand sets of holding rolls b and enters the space between thelefthand rolls c (corresponding to the leftmost set of rolls 12a shownin FIG. 1). These rolls 0 are rocked by the drive shaft so that theymove out of registry with the holding rolls b and subject successiveportions of the workpiece 37 to the action of a bending force which isrelatively strong but too weak to deform the material of the workpiecebeyond the elastic limit. This initial force is indicated in FIG. 9 bythe reference character P1. The thus initially stressed portion of theworkpiece 37 then enters the space between the rolls d which correspondto the set of median rolls 12a in FIG. 1 and which subject the workpieceto the action of a relatively weak additional or final bending force P2which is strong enough to deform the material of the workpiece beyondthe elastic limit so that the deformation of the workpiece is permanent.The second set of rolls 0 shown in FIG. 9 corresponds to the rightmostset of rolls 12a shown in FIG. 1, and these rolls (2 again subject theworkpiece 37 to the action of bending forces P1, i.e., the applicationof the final or additional bending force P2 takes place upon a portionof the workpiece located between two spaced portions which are subjectedto the action of initial bending forces -P1. The rolls a, b, c, d ofFIG. 9 also hold the workpiece 37 against rotation and, since the rollsb, c and d are disposed in sets of four each so that each side of arectangular workpiece is engaged by one such roll, the workpiece may besimultaneously deformed in two directions, namely, in a horizontal andin a vertical plane.

The just described method of straightening or deforming the workpieces37 insures that the bending or straightening operation cannot result indenting or other damage to the walls of a tubular workpiece. It wasfound that such denting normally takes place if an advancing workpieceis immediately subjected to the action of bending forces which arestrong enough to plasticize the material, i.e., to stress the materialbeyond the elastic limit. However, and due to the fact that the improvedmachine generates bending or deforming stresses in a plurality ofstages, the walls of relatively thin-walled tubular Workpieces will notbuckle and will not develop dents or similar depressions.

It was also found that the force P2 may be relatively small, at leastwhen compared with the forces P1. For example, and if a workpiece 37having a given profile and a given wall thickness can be deformed closeto the elastic limit of its material by the application of initialforces in the range of 5,000 mp., the additional force P2 need notexceed 1,500 mp., i.e., it can be a small fraction of the initial force.

The optimum distance e between the rolls b, c, d can be readilydetermined by simple experimentation. Such distance e will depend on thewall thickness of workpieces 37, on the width and height of theworkpieces, and on the nature of the material of the workpieces. Thesame holds true for the magnitude of forces P1 and P2. The rolls b whichcorrespond to the rolls 12 of FIG. I serve to hold in the predeterminedpath such portions of the workpiece 3-7 which have advanced beyond thefeed rolls a (corresponding to rolls 3a-3c) and which are about to enterthe gaps between the withdrawing rolls a (corresponding to the rolls3d-3e of FIG. 1).

The various adjusting units of the machine shown in FIGS. 1 to 8 enablethe operators to select the magnitude of bending forces P1 and P2 in avery simple and timesaving manner as well as with a requisite degree ofaccuracy, not only when the machine is idle but also in actual use. Thelatter feature is of particular advantage because the operators canvisually observe or measure the deformation of workpieces and thereuponadjust the apparatus if the actual deformation exceeds or is less thanan optimum deformation of the stock. Furthermore, the feature that themachine is adjustable in actual use saves much time when the workpieces37 are treated one after the other in rapid sequence because theoperation need not be interrupted at all but can proceed at full speedduring adjustment of one or more carriers 11 and/ or 11a. Also, suchconstruction enables my machine to process large numbers of workpieceswithout necessitating the provision of intermediate magazines whichconstitute essential components of many presently known straighteningmachines. Such magazines are normally provided upstream of the feedrolls, such as the rolls 3a-3c of my machine, to accommodate stockdelivered by a continuously operating supply conveyor when aconventional straightening machine is brought to a standstill becauseits straightening rolls require adjustment.

The extent of movement of stressing means including the straightening orbending rolls 12a and their carriers 11a is controlled by eccentricrings 19 which are rotated by the drive shaft 15 and whose throw can beselected by the adjusting members 14. In heretofore known machines, thethrow of such eccentrics can be adjusted only when the machine is idle.In my machine, the operators can select the throw of rings 19 by thesimple expedient of starting the respective motors 24b and by thuschanging the position of corresponding adjusting members 14 in the axialdirection of the drive shaft 15. By rotating the worms 24, the motors24b can alter the throw of eccentric rings 19 in an exceptionally simpleand time-saving manner without interfering with the travel of workpieces37 along the path defined by the rolls 312-31". The eccentricity ofrings 19 determines the strokes of the carriers 11a and the magnitude offorces P1 and P2.

If the cross-sectional area of a workpiece 137 is very large, one canresort to a method which will now be described with reference to FIG.10. This method is carried out by resorting to an apparatus which canapply to successive portions of workpieces 137 initial forces P1, P3 intwo successive stages whereby the first application of the forces P3precedes the application of the additional or final force P2. The forceP3 is just strong enough to effect deformation of the material beyondthe elastic limit whereas the forces P1, P2 together bring about adeformation close to the elastic limit. Of course, the teaching of FIG.can be carried still further by subjecting each successive portion ofthe workpiece 137 (or of a still heavier workpiece) to the action ofthree or more different initial forces and of thereupon subjecting thethus prestressed portions to the action of the final force P2 to bringabout permanent deformation of the material.

The preceding description speaks of bending or straightening rolls, of abending or straightening machine and of bending or straightening forcesbecause the method and machine of my invention may be utilized tostraighten a bent workpiece, to bend a straight workpiece, or to changethe curvature of a bent workpiece. Therefore, the appended claims referto a method or machine for changing the curvature of elongatedworkpieces whereby the original curvature may be zero or the curvatureof the properly treated workpiece may be zero.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of my contribution to the art and, therefore suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. A method of changing the curvature of elongated workpiecesparticularly tubular workpieces of other than circular cross-sectionaloutline comprising the steps of advancing the workpieces lengthwisealong a predetermined path, subjecting successive portions of advancingworkpieces first to the action of initial bending forces to stress suchportions to slightly below the elastic limit of their material; andthereupon subjecting the initially stressed portions to the action ofadditional bending forces to stress such portions beyond the elasticlimit of their material and to thus effect permanent deformation of therespective workpieces.

2. A method as set forth in claim 1 further comprising the step ofholding the workpieces against turning during travel along saidpredetermined path.

3. A method as set forth in claim 2 wherein the magnitude of saidadditional bending forces is a fraction of the magnitude of said initialbending forces.

4. A method as set forth in claim 2, wherein said initial bending forcesare applied in a plurality of successive stages so that each successiveportion of a workpiece advancing along said path is subjected tostresses generated by more than two different bending forces.

5. A method as set forth in claim 2, wherein each successive portion ofa workpiece advancing along said path is subjected to the action ofinitial and additional bending forces acting upon the workpiece in aplurality of directions substantially transversely of the workpiece.

6. A method as set forth in claim 1, wherein said workpieces aremetallic tubes of rectangular cross-sectional outline.

7. A method as set forth in claim 1, wherein said advancing stepcomprises guiding the workpieces between sets of cooperating rollsdefining said predetermined path and wherein the application of saidinitial and additional bending forces is carried out by changing theposition of selected sets of such rolls.

8. A method as set forth in claim 1, wherein the application of saidadditional bending forces takes place upon a portion of a workpiecedisposed between two portions which are subjected to the action of saidinitial bending forces.

9. A method as set forth in claim 8, further comprising the step ofchanging the magnitude of said initial bending forces while theworkpieces advance along said path.

10. A method as set forth in claim 8, further comprising the step ofchanging the magnitude of said additional bending forces while theworkpieces advance along said path.

11. A machine for changing the curvature of elongated workpieces,particularly for straightening of elongated tubular workpieces of otherthan circular cross-sectional outline, comprising advancing means formoving the workpieces lengthwise along a predetermined path; firststressing means for subjecting successive portions of moving workpiecesto the action of initial bending forces to stress such portions toslightly below the elastic limit of their material; and second stressingmeans for subjecting the initially stressed portions of moving workpieceto the action of additional bending fonces to stress such portionsbeyond the elastic limit of their material and to thus effect permanentdeformation of the workpieces.

12. A machine as set forth in claim 11, wherein each of said stressingmeans comprises at least one set of work-engaging rolls, carrier meansfor such set of rolls, and drive means for moving said carrier meansthrough distances of predetermined length substantially transversely ofsaid path whereby the rolls apply bending forces to the workpieces insaid path.

13. A machine as set forth in claim 12, wherein said drive means isarranged to move the rolls which respectively apply to moving workpiecesinitial and additional bending forces through different distances.

14. A machine as set forth in claim 13, wherein said sets of rolls formtwo spaced groups of rolls which apply initial bending forces and afurther group of rolls which apply said additional bending forces, saidfurther group of rolls being disposed between said spaced groups.

15. A machine as set forth in claim 12, further comprising adjustingmeans for regulating said distances while the workpieces are advancedalong said path so that the magnitude of said initial and additionalbending forces can be altered when the machine is in actual use.

16. A machine as set forth in claim 15, wherein said adjusting meanscomprises a two-armed lever for each of said carrier means, each of saidlevers being rockable about an axis which is substantially parallel withsaid path and each having a first arm connected with the respectivecarrier means and a second arm, an eccentric received in said secondarm, an adjusting member rotatably received in and arranged to changethe throw of said eccentric in response to axial movement with referenceto the eccentric, and means for axially moving said adjusting member.

17. A machine as set forth in claim 16, wherein each of said adjustingmembers comprises a pair of parallel inclined external faces abuttingagainst similarly inclined internal faces of the respective eccentricand the means for axially moving said adjusting members comprises a gearfor each of said adjusting members, prime movers for rotating said gearsin either one of two opposite directions, and racks provided on saidadjusting members and meshing with the respective gears.

18. A machine as set forth in claim 17, further comprising antifrictionbearing means interposed between each of said adjusting members and therespective rack.

19. A machine as set forth in claim 16, further comprising a commonrotary drive shaft for said adjusting members and means securing saidadjusting members for axial movement with reference to and for angularmovement with said drive shaft.

20. A machine as set forth in claim 16, further comprising means foradjusting the position of pivot axes for said levers.

21. A machine as set forth in claim 16, further comprising holding rollsadjacent to said path upstream of said initial force applying rolls,carrier means for said holding rolls, and means for adjusting theposition of said last named carrier means transversely of said path.

22. A machine as set forth in claim 11, wherein said advancing and saidstressing means comprise rolls arranged to hold the workpieces againstrotation during travel along said path.

23. A machine as set forth in claim 22, wherein said first stressingmeans comprises means for applying said initial bending forces in aplurality of stages.

24. A machine as set forth in claim 22, wherein said first stressingmeans comprises two spaced portions and said second stressing means isdisposed between such portions of said first stressing mean.

10 MILTON S.

References Cited UNITED STATES PATENTS Davis 72-160 Haskin 72-164Abramson 72-164 Smith 72-168 Mason 72-164 X Siegerist 72-164 X MEHR,Primary Examiner.

US. Cl. X.R.

